1. Field of the Invention
The present invention relates to an image-holding member employing a resin having a specified structure, more particularly to an image-holding member having excellent surface slipperiness and excellent durability.
The present invention also relates to an electrophotographic apparatus, an apparatus unit, and a facsimile machine employing the above image-holding member.
2. Related Background Art
A typical image-holding member is an electrophotographic photosensitive member. In recent years, many types of electrophotographic photosensitive members employing an organic photoconductive material have been reported and have come to be practically used because of their non-pollution causing property, high productivity, ease of material design, and expected future growth. Naturally, the electrophotographic photosensitive members are required to have suitable electrical, mechanical, optical and other properties depending on the electrophotographic process employing the members. In particular, the photosensitive members which are used repeatedly are required to be durable against the external electrical and mechanical force such as corona discharge, imagewise exposure, toner development, transfer onto paper, and cleaning treatment which act on the surface of the photosensitive member. Specifically, required is the durability not causing the deterioration with ozone generated on corona charging, such as decrease of the sensitivity and the potential, and increase of the residual potential, not receiving the abrasion and scratching on the surface by the friction during image-transfer and cleaning.
The surface of the photosensitive member is generally made of an extremely thin resin layer, so that the properties of the surface resin is of great importance. Polycarbonate resins having bisphenol A skeleton have been used as the resin satisfying the aforementioned conditions. The polycarbonate resins, however, do not completely satisfy all of the electrophotographic properties required to the resin for the photosensitive member. For example, a bisphenol A type polycarbonate resin, which has relatively high crystallinity, is liable to become gel, when solubilized in a solvent. Therefore, the electrophotographic photosensitive member employing this resin tends to give inferior electrophotographic characteristics Or to result in low productivity. This resin shows low slipperiness to a usual elastic blade of the cleaning means. Therefore, when this resin is used as the surface layer of a photosensitive member, the reversal of the cleaning blade and thus incomplete cleaning tends to occur, and the abrasion of the surface of the member is liable to be accelerated by the relatively high frictional resistance of the transferred material in the image transfer step.
In one method for solving the above problems, a certain component is introduced to the polycarbonate structure to form a copolymer for the purpose of lowering the crystallinity and improving the liquid storability (Japanese Laid-Open Patent Application No.61-62039, etc.). In this method, however, according to the copolymerized component, the electrophotographic characteristics, the mechanical properties of the copolymer, or coating application property may sometimes be impaired. Therefore, this method is not necessarily satisfactory.
In another method, a surfactant mainly composed of a polydimethylsiloxane resin is added to the resin to improve the coating application property. In this method, however, even an extremely small amount of the surfactant may cause a remarkable increase of the residual potential. In particular, the addition of a less compatible organosiloxane derivative deteriorates the optical properties, the image quality, or the durability of the coating layer.
In still another method, polyorganosiloxane block is incorporated into the polycarbonate resin by copolymerization to improve the above-mentioned properties as disclosed in Japanese Laid-Open Patent Application No.61-132954. In this method, as the polymer itself exhibits slipperiness, it hardly changes during repeated use. However, the polymer cannot be steadily produced because the solution thereof in a solvent becomes turbid in white, and a mixture of a homopolymer of the polyorganosiloxane with a homopolymer of the employed polyhydric phenol is formed simultaneously.
In still another method, a bisphenol Z type polycarbonate resin is used to improve the above properties. Electrophotographic photosensitive members are being investigated further to meet requirement for higher image quality and higher durability in recent years.
Similar problems are involved also in other types of image-holding members such as those used for electrostatic recording mediums and image-holding members for engraving.